1. Field of the Invention
The present invention relates to a fluid-filled vibration-damping device used for an engine mount of an automobile or the like.
2. Description of the Related Art
A vibration-damping device has been known as a kind of device such as a vibration-damping connecting body or a vibration-damping support body to be interposed between members constituting a vibration transmission system to connect the members to each other in a vibration-damping manner. Additionally, as disclosed in U.S. Pat. No. 8,556,239, a fluid-filled vibration-damping device is proposed as a vibration-damping device to obtain high vibration-damping performance owing to the flowing action of a fluid sealed inside. This fluid-filled vibration-damping device comprises a first mounting member, a second mounting member, a main rubber elastic body elastically connecting them to each other, a partition member supported by the second mounting member, a pressure-receiving chamber and an equilibrium chamber which are defined to both sides of the partition member with a non-compressible fluid sealed therein, and an orifice passage communicating the pressure-receiving chamber and the equilibrium chamber with each other. A vibration input between the first mounting member and the second mounting member causes relative pressure fluctuation therebetween, thereby generating a fluid flow through the orifice passage, so that the vibration-damping effect is exerted based on the resonance action of the fluid.
The fluid-filled vibration-damping device exerts excellent vibration-damping effect based on the flow action of the fluid upon input of a vibration to whose frequency the orifice passage is tuned in advance. On the other hand, upon input of a vibration in a higher frequency range than the tuning frequency of the orifice passage, the device suffers from a deterioration of vibration-damping performance (vibration insulating action) caused by antiresonance of the orifice passage.
Some documents including U.S. Pat. No. 8,556,239 disclose a fluid-filled vibration-damping device further comprising a communication passage provided at the partition member to communicate the pressure-receiving chamber and the equilibrium chamber with each other, with a movable rubber film being disposed in the communication passage such that a liquid pressure of each of the pressure-receiving chamber and the equilibrium chamber is applied on the respective face of the movable rubber film. According to this, upon input of an idling vibration or the like with a higher frequency and a smaller amplitude than the tuning frequency of the orifice passage, which is set to a low frequency corresponding to an engine shake, the movable rubber film is elastically deformed to generate a substantial fluid flow between the pressure-receiving chamber and the equilibrium chamber via the communication passage. This ensures absorption or moderation of the inner pressure fluctuation of the pressure-receiving chamber, so that the vibration insulating effect owing to lower dynamic spring is exerted. Upon input of a low-frequency large-amplitude vibration to which the orifice passage is tuned, elastic deformation of the movable rubber film cannot follow it completely, thereby causing a fluid flow via the orifice passage to favorably exhibit the vibration-damping effect based on the flow action of the fluid.
It is also possible to assertively use the substantial fluid flow between the pressure-receiving chamber and the equilibrium chamber through the communication passage caused by elastic deformation of the movable rubber film to improve the vibration-damping performance for a vibration in a higher frequency range than an idling vibration. Specifically, it is possible to generate a fluid flow via the communication passage accompanying elastic deformation of the movable rubber film in a resonance state, upon input of a vibration in a middle to high frequency range of approximately 50 to 100 Hz generally corresponding to the driving rumble for example, thereby assertively improving the vibration insulating performance owing to lower dynamic spring based on the resonance action of the flowing fluid.
Incidentally, in order to more advantageously obtain the above-described low dynamic spring action owing to elastic deformation of the movable rubber film upon a middle-frequency middle-amplitude vibration like an idling vibration of an automobile, it is desirable that the thin-walled part of the movable rubber film allowed to elastically deform have a large area. In other words, in the structure of the device according to U.S. Pat. No. 8,556,239, the sizes of the retaining parts at the center and the outer rim to be clamped by the partition member and the sizes of the reinforcing crosspieces extending in a radial fashion as connecting the retaining parts may be reduced in a plan view for example, to increase the area of the thin-walled film part. The resultant movable rubber film is more likely to exhibit the pressure absorbing action owing to its deformation, favorably obtaining the vibration-damping effect by lower dynamic spring.
However, simply increasing the area of the thin-walled film part of the movable rubber film by the means of using reinforcing crosspieces with small width dimensions or reducing the diameter of the outer peripheral retaining part etc., leads to a lower dynamic spring in the whole of the movable rubber film. This may damage the vibration-damping ability owing to the orifice passage in relation to a low-frequency large-amplitude vibration. In addition, a fluid flow via the communication passage accompanies the displacement of the movable rubber film, leading to a problem of higher dynamic spring due to antiresonance of the fluid flow in relation to the vibration in a higher frequency range of approximately 100 to 200 Hz like a high-speed driving rumbling or an acceleration driving rumble of an automobile etc., which may deteriorate the vibration-damping performance.